Synthetic aircraft turbine oil

ABSTRACT

Synthetic lubricating oil composition comprising a major portion of an aliphatic ester-base oil having lubricating properties formed from the reaction of a pentaerythritol or trimethylolpropane and an organic monocarboxylic acid containing a thio-oxazolidinedione, a thiazolidinedione or the corresponding amine salt.

United States Patent Patmore et al.

[ Dec. 18, 1973 SYNTHETIC AIRCRAFT TURBINE OIL Inventors: Edwin L. Patmore, Fishkill;

Frederick G. Oberender, Wappingers Falls; David D. Reed, Lagrangeville, all of NY.

Assignee: Texaco Inc., New York, NY.

Filed: Aug. 21, 1972 Appl. No.1 282,182

US. Cl 252/33.6, 252/4715,'252/402, 260/307 C Int. Cl. C10m l/38, ClOm l/32 Field of Search 252/336, 56 S, 47.5, 252/402; 260/307 C References Cited UNITED STATES PATENTS 6/1957 Kluge et a1 252/475 6/1957 Watson et a1... 252/47.5 6/1957 Levin 252/475 2,800,491 7/1957 Ellis r ..252/47 5 3,249,543 5/1966 Wilson ..252/47.5

FOREIGN PATENTS OR APPLICATIONS 1,180,387 2/1970 Great Britain OTHER PUBLlCATlONS Cohen Ind. Eng. Chem. Vol. 45 (1953), pages 1766-1774.

Primary ExaminerDaniel E. Wyman Assistant ExaminerW. Cannon 1 Attorney-Thomas H. Whaley et a1.

10 Claims, No Drawings SYNTHETIC AIRCRAFT TURBINE OIL BACKGROUND OF THE INVENTION This invention is concerned with a lubricating oil composition for gas turbine or jet engines. Gas turbine engines employed in aircraft are operated under extreme environmental conditions. The lubricating oil must be fluid under sub-zero temperatures and must be thermally stable, non-corrosive and possess loadcarrying and anti-wear properties at engine temperatures of 400 to 500F. or above. The environmental and operating conditions put such a severe stress on the lubricating oil for a turbine engine that the most advanced mineral lubricating oil compositions cannot be employed in these engines. It is conventional to employ synthetic ester-base lubricating oil compositions containing suitable augmenting additive combinations for lubricating turbine engines. The ester-base oils are operative over a wide temperature range and exhibit good thermal stability, anti-wear, and oxidation-resistant properties while providing effective lubrication.

Newer and more powerful gas turbine engines designed to provide advanced levels of supersonic flight are under development. These engines put increasing stresses on the lubricating oil composition and improved oil compositions must be provided to meet the load-carrying, anti-wear, oxidation resistance and corrosion resistance requirements at higher levels of oxidative and thermal stress.

DESCRIPTION OF THE PRIOR ART U.S. Pat. No. 2,796,402 discloses grease and lubricating oil compositions having extreme pressure properties containing rhodanine and its five-substituted compounds.

U.S. Pat. No. 2,796,403 discloses grease and lubricating oil compositions including synthetic lubricants having extreme pressure properties containing three-hydrocarbon-substituted rhodanines.

U.S. Pat. No. 2,796,404 discloses lubricating oil compositions including synthetic lubricants of the ester or ether type having extreme pressure and anti-corrosive properties containing alkylaminobenzylidenerhodanine.

SUMMARY OF THE INVENTION The synthetic lubricating oil composition of the invention comprises a major portion of an aliphatic esterbase oil having lubricating properties formed from the reaction of a pentaerythritol or trimethylolpropane and a mixture of hydrocarbyl monocarboxylic acids containing an effective load-carrying amount of a thiooxazolidinedione, thiazolidinedione or corresponding amine salt represented by the formulas:

in which X represents sulfur when Y represents oxygen. and X represents oxygen when Y represents sulfur, and R represents a hydrocarbyl radical having from about four to 24 carbon atoms. In general, the compounded fluid will also contain an alkylphenyl or alkarylphenyl naphthylamine, a dialkyldiphenylamine. a polyhydroxyanthraquinone and a hydrocarbyl phosphate defined below.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Thio-oxazolidinedione and thiazolidinedione suitable for the synthetic lubricating oil composition are represented by the following formula:

in which X is sulfur when Y represents oxygen, and X is oxygen when Y represents sulfur. The corresponding amine salts have the formula:

where X and Y have the same values and R is a hydrocarbyl radical having from about four to 24 carbon atoms. The preferred amine salts are those in which R is an alkyl or aliphatic radical having from about 12 to 22 carbon atoms with the most preferred being those in which R is an aliphatic radical having from about 18 to about 22 carbon atoms.

Methods for preparing the prescribed thio-oxazolidinedione, thiazolidinedione and the corresponding amine salts are well known. The preparation of 2,4- oxazolidine-dione is described in Chemical Abstracts, 50, 9387,, and in J. Am. Chem. Soc., 80,973 (1958).

The following examples illustrate the preparation of a representative number of the prescribed compounds which can be employed in the synthetic aircraft turbine oil compositions of this invention.

EXAMPLE I 2Thi0-Oxazolidinedione Formaldehyde (40 mls. of a 37 percent solution) was added with stirring and cooling (temperature held at 10C.) to a solution of sodium thiocyanate (40.5 g.) and sodium cyanide (27.0 g.) in water (55 mls.). Concentrated hydrochloric acid was added while maintaining the temperature at 10C. The reactants were allowed to warm to room temperature and set overnight. Solids were removed by filtration and the filtrate was heated at reflux for 1.5 hours. Extraction with ether (5 X ml.), concentration on the rotary evaporator, and two recrystallizations from water gave 7.] g. of product, m.p. l079C. (lit. m.p. l 13C.).

EXAMPLE ll 2,4-Thiazolidinedione A reaction mixture of pseudothiohydantoin (6.4 g.) and hydrochloric acid (50 ml. conc. HCl/lSO mls. of water) was heated at reflux for 6 hours, concentrated on the rotary evaporator, and treated with 50 mls. of methanol. The ammonium chloride was removed by filtration and the filtrate concentrated to give 5.4 g. of crude product. Recrystallization from ethanol gave 4.2 g. of product, m.p. l24126C. (lit. m.p. l26,l27C.).

EXAMPLE III 2,4-Oxazolidinedione A sodium ethoxide solution was prepared from sodium (9.2 g.) and anhydrous ethanol (200 mls.). This solution was cooled while ethyl glycolate (41.6 g.) and urea (24.0 g.) were added. The reaction mixture was heated to reflux and held there 15 minutes before concentration on the rotary evaporator. The solid residue was dissolved in 120 mls. of water and the aqueous solution extracted with 75 mls. of ether. The aqueous solution'was then acidified, extracted with four 75 ml. portions of ether, the ether extracts combined and concentrated on the rotary evaporator to yield the crude product. Recrystallization from ethanol afforded 5.3 g. of product, m.p. 8788C. (lit. m.p. 89-90C.).

EXAMPLE IV t'C18-C22'Alky1 Primary Thiazolidinedione t-C -C Primary amine (31.5 g.) was added to a stirred solution of 2,4-thiazolidinedione (11.7 g.) in benzene (7O mls.) and the reactants were heated at 50C. for 1 hour. The reaction mixture was concentrated on the rotary evaporator at 165F. and aspirator pressure and then under vacuum pump pressure to give 41.5 g. of product. Neut. No. 134 (calc. 130).

EXAMPLE V Primary Amine Salt of 2-Thio- Amine Salt of 2,4-

t-C -C Alkyl Oxazolidinedione t-C -C Alkyl primary amine (21.4 g.) and 2-thiooxazolidinedione (8.0 g.) were heated together in benzene (50 mls.) for 1 hour at 50C. Concentration on the rotary evaporator at 165F. at vacuum pump pressures gave 29 g. of product. Neut. No. 120 (calc. 129).

Examples of other compounds within the prescribed classes which can be employed in the synthetic aircraft turbine oil composition of this invention include the following: n-Butyl, n-hexyl, Z-ethylhexyl, n-decyl-, 1 or 2-naphthyl,-tris-(2-ethylhexyl)amine salts of thiooxazolidinediones or thiazolidinediones, the benzylidene, S-heptylidene etc. derivatives of thiooxazolidinedione or thiazolidinediones and their amine salts and the -benzyl, S-phenyl, S-methyl etc. derivatives and amine salts of these materials can be used.

The prescribed compounds are employed in the lubricating oil composition in an amount ranging from about 0.01 to 5 weight percent. In general, amounts ranging from about 0.05 to 0.5 percent are effective and are preferred for imparting load-carrying and corrosion resistance properties to the lubricant compositron.

The base fluid component of the lubricant of the invention is an ester-base fluid prepared from pentaerythritol or trimethylolpropane and a mixture of hydrocarbyl monocarboxylic acids. Polypentaerythritols, such as dipentaerythritol, tripentaerythritol and tetrapentaery-thritol can also be employed in the reaction to prepare the base oil.

The hydrocarbon monocarboxylic acids which are used to form the ester-base fluid include the straightchain and branched-chain aliphatic acids, cy'cloali phatic acids and aromatic acids, as well as mixtures of these acids. The acids employed have from about two to about 18 carbon atoms per molecule, and preferably from about five to 10 carbon atoms. Examples of suitable specific acids are acetic, propionic, butyric, valeric, isovaleric, caproic, decanoic, hexadecanoic, pelargonic, dodecanoic, cyclohexanoic, naphthenic, tertiary-butylacetic acid and 2-ethylhexanoic acid.

In general, the acids are reacted in proportions leading to a completely esterified pentaerythritol or trimethylolpropane with the preferred ester bases being the pentaerythritol tetraesters. Examples of such commercially available tetraesters include pentaerythritol tetracaproate, which is prepared from purified pentaery-thritol and crude caproic acid containing other C monobasic acids. Another suitable tetraester is prepared from a technical grade pentaerythritol and a mixture of acids comprising about percent valeric, 12 percent Z-methyl pentanoic, 27 percent caprylic, 15 percent pelargonic, 9 percent heptylic, 5 percent caproic and minor amounts of iso-valeric and capric acids. Another effective ester is the triester of trimethylolpropane in which the trimethylolpropane is esterified with a mono-basic acid mixture consisting of 2 percent valeric, 9 percent caproic, 13 percent heptanoic, 7 percent octanoic, 3 percent caprylic, percent pelargonic and 1 percent capric acids. Trimethylolpropane triheptanoate, trimethylolpropanepentanoate and trimethylolpropanehexanoate are also suitable.

ester bases.

The ester base comprises the major portion of the formulated synthetic ester-base lubricating oil composition. In general, this ester-base fluid is present in a concentration ranging from about to 98 percent of the composition.

The effectiveness of the lubricating oil compositions of the invention is enhanced by the addition of other additives to the oil composition. Alkyl or alkaryl phenyl naphthylamines are highly effective anti-oxidants for synthetic lubricating oils. These compounds are represented by the formula:

ditive is an amount from about 0.5 to 2.5 weight percent.

Another effective anti-oxidant for the lubricating oil composition of the invention is a dialkydiphenylamine represented by the formula:

in which R is an alkyl radical having from about four to 12 carbon atoms. Examples of these amines include dioctyldiphenylamine didecyldiphenylamine, didodecyldiphenylamine, dihexydiphenylamine and similar compounds. Dioctyldiphenylamine is the preferred compound and the preferred concentration is from about 0.5 to 2.0 percent.

An effective metal deactivator for a synthetic lubricating oil composition is a polyhydroxyanthraquinone. Suitable compounds in this class are the dior polyhydroxy-anthraquinones, such as 1,4-dihydroxyanthraquinone, also known as quinizarin, 1,5-dihydroxyanthraquinone and 1,S-di-hydroxyanthraquinone, and the higher polyhydroxyanthraquinones. The preferred concentration of this component is from about 0.01 to 0.5 weight percent.

A valuable anti-wear component for a synthetic lubricating oil composition is a hydrocarbylphosphate ester, represented by the formula (RO) -,PO, in which R is a hydrocarbyl radical having from two to 12 carbon atoms. The hydrocarbyl radical can be an alkyl, aryl, alkaryl, cycloalkyl or aralkyl radical of the prescribed carbon chain length, although radicals having from four to 8 carbon atoms are preferred. Effective compounds include tricresyl phosphate, cresyl di-phenyl phosphate, triphenylphosphate, tributylphosphate, tris- (2-ethylhexyl) phosphate and tricyclohexylphosphate. These compounds are generally employed in a lubricating oil composition in a concentration ranging from about 0.5 to 5 percent.

It is conventional to employ minor amounts of an anti-foam additive in the synthetic lubricating oil composition. Effective anti-foamants are the silicone fluids, such as dimethyl silicone and diethylsilicone and these are generally employed at a concentration ranging from about 5 to 200 ppm parts per million.

The lubricating oil composition of the invention was tested for its load-carrying properties in the Ryder Gear Test. This test was conducted in accordance with Federal Test Method Standard 791, Test Method 6508. The base fluid blend employed for conducting the tests consisted of a commercial ester base from pentaerythritol and a mixture of C to C fatty acids containing 0.10 weight percent quinizarin, 1.00 weight percent p,- p'-di-tert.-octyldiphenylamine, 1.50 weight percent N- (4-tert.-octylphenyl)-l-naphthylamine, 2.00 weight percent tricresyl phosphate and 50 ppm of a dimethyl silicone fluid.

The results of the Ryder Gear Test are given in Table I below:

TABLE I RYDER GEAR LOAD-CARRYING TEST Blend Identification 2 Example! 0.15 3325 3 Example 11 0.20 3560 4 Example lll 0.15 2560 5 Example IV 0.3 3155 6 Example V 0.3 2930 Runs 2, 3, 5 and 6 demonstrate that the novel synthetic ester-base lubricating oil compositions containing the prescribed thio-oxazolidinedione and thiazolidinedione and the corresponding amine salts of the invention possess substantially improved load-carrying properties as compared to both the Base Blend and to the fully formulated fluid of Run 4. Run 4 illustrates that the all-oxygen analog of Example 111 is totally ineffective as a load-carrying additive in these lubricants.

We claim:

1. A synthetic lubricating oil composition comprising a major portion of an aliphatic ester-base oil having lubricating properties formed from the reaction of a pentaerythritol or trimethylolpropane and a saturated hydrocarbyl monocarboxylic acid having from about 2 to 18 carbon atoms per molecule containing from about 0.01 to 5 weight percent of an oxazolidinedione, thiazolidinedione or the corresponding amine salt represented by the formulas:

in which X represents S when Y is O, and X represents 0 when Y is S and R represents a hydrocarbyl radical having from about four to 24 carbon atoms.

2. A lubricating oil composition according to claim 1 in which R represents an aliphatic hydrocarbon radical having from about 12 to 22 carbon atoms.

3. A lubricating oil composition according to claim 1 containing from about 0.05 to 0.5 weight percent of said thio-oxazolidinedione, thiazolidinedione or corresponding amine salt.

4. A lubricating oil composition according to claim 1 in which R is a t-C -C primary alkyl radical.

5. A lubricating oil composition according to claim 1 containing 2-thio-oxazolidinedione.

6. A lubricating oil composition according to claim 1 containing a 2,4-thiazolidinedione.

7. A lubricating oil composition according to claim 1 containing the tC, C primary amine salt of 2,4- thiazolidinedione.

8. A lubricating oil composition according to claim 1 containing the tC, C alkyl primary amine salt of 2-thio-oxazolidinedione.

9. A lubricating oil composition according to claim 1 containing from about 0.5 to 2.5 percent of an alkylphenyl naphthylamine, from about 0.5 to 2.0 percent of dialkyldiphenylamine, from about 0.01 to 0.5 percent of a polyhydroxyanthraquinone and from about 0.5 to 5 percent of a hydrocarbyl phosphate ester.

10. A lubricating oil composition according to claim 1 in which said ester-base oil is formed from the reaction of pentaerythritol and a mixture of C to C saturated fatty acids. 

2. A lubricating oil composition according to claim 1 in which R represents an aliphatic hydrocarbon radical having from about 12 to 22 carbon atoms.
 3. A lubricating oil composition according to claim 1 containing from about 0.05 to 0.5 weight percent of said thio-oxazolidinedione, thiazolidinedione or corresponding amine salt.
 4. A lubricating oil composition according to claim 1 in which R is a t-C18-C22 primary alkyl radical.
 5. A lubricating oil composition according to claim 1 containing 2-thio-oxazolidinedione.
 6. A lubricating oil composition according to claim 1 containing a 2,4-thiazolidinedione.
 7. A lubricating oil composition according to claim 1 containing the t-C18-C22 primary amine salt of 2,4-thiazolidinedione.
 8. A lubricating oil composition according to claim 1 containing the t-C18-C22 alkyl primary amine salt of 2-thio-oxazolidinedione.
 9. A lubricating oil composition according to claim 1 containing from about 0.5 to 2.5 percent of an alkylphenyl naphthylamine, from about 0.5 to 2.0 percent of dialkyldiphenylamine, from about 0.01 to 0.5 percent of a polyhydroxyanthraquinone and from about 0.5 to 5 percent of a hydrocarbyl phosphate ester.
 10. A lubricating oil composition according to claim 1 in which said ester-base oil is formed from the reaction of pentaerythritol and a mixture of C5 to C9 saturated fatty acids. 